hhmm, i do believe there is more torque in lower gears and torque will cause the clutch to slip before HP, look if you are Toyota guys and know the 22re, you slip a brand new clutch in 4th or 5th, you need to start looking at installation mess ups.
and that the stock clutch was never meant to have a double down low load attached to it.
the other problem he might have is a miss adjusted push rod on his clutch, or if he has a master cylinder from a cheap auto parts store it might not be releasing his clutch all the way, but your torque is going to spin the clutch before your 4th and 5 th gears just driving down the road.
I agree with Glen...There's more load on the clutch in High range with the trans in 3rd or 4th than in any of the Low ranges in the T-case. It's just isn't possible that the clutch would slip in low and not in the high ranges while street driving....UNLESS, you're referring to downhill descents in low with no throttle input and the vehicle could move faster than the engine can brake via the clutch.
and just to clarify....Manual transmissions don't slip, clutches do.
the topic of the thread is about a slipping clutch, to me that means a manual not auto trans